In research for improving ambient lighting systems and smart light management systems of today, there is an ambition to provide flexible user friendly solutions in which the user may determine the atmosphere created by a number of luminaries. In general, a room is illuminated with a multiple of distributed luminaries, and an intelligent light control system will be able to measure and control the lighting characteristics of each individual luminary. For this to be realized, two conditions should be met. One is the availability of light sources with tunable color and intensity. The maturing of LED technology has resulted in light sources that fulfill this demand. The other prerequisite is a control feedback system that measures the intensity and color of the individual luminaries simultaneously. In order to achieve this, optical sensors are required, for instance to measure the flux, the color point, the color rendering index, or even the full spectral distribution of the light illuminating a certain part of the room. In addition one would like to be able to measure what light source is illuminating which part of the room. When the fixture position of the light source is fixed and the light can be directed to different positions for instance with a beam steering technique, the source position of the light sources can be detected by measuring the angle under which the light beam hits the target position.
In addition optical sensors, which are coated with interference filters have an angular dependency in their spectral responsivity, which makes it difficult to make absolute wavelength measurements of light incident from many angles, i.e. diffuse light, with said optical sensors.
Patent application publication US 2004/0119908 A1 discloses a liquid crystal modulator device capable of accurate control of light from a light source. The device comprises R, G and B light emitting diodes, LEDs, a light guide plate for guiding and diffusing, i.e. mixing, light from the colored LEDs, and an optical sensor for each color of the light for measuring the mixed colored light in the light guide plate. To get an accurate light measurement of the mixed colored light in the light guide plate, direct light from the LEDs is blocked from reaching the individual optical sensor by providing the sensor with an incident light angle limiting device realized as a through hole in an absorbing piece of material. However, the solution is only applicable in a static environment where the color, position and light direction from each light source and the position, and orientation of the light sensors of such a system are fixed.